feat: add MonitorServer with /healthz and /varz endpoints

src/NATS.Server/NatsServer.cs

@@ -3,6 +3,7 @@ using System.Net;
 using System.Net.Sockets;
 using System.Text;
 using Microsoft.Extensions.Logging;
+using NATS.Server.Monitoring;
 using NATS.Server.Protocol;
 using NATS.Server.Subscriptions;
 
@@ -19,6 +20,7 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
     private readonly ServerStats _stats = new();
     private readonly TaskCompletionSource _listeningStarted = new(TaskCreationOptions.RunContinuationsAsynchronously);
     private Socket? _listener;
+    private MonitorServer? _monitorServer;
     private ulong _nextClientId;
     private long _startTimeTicks;
 
@@ -61,6 +63,12 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
 
         _logger.LogInformation("Listening on {Host}:{Port}", _options.Host, _options.Port);
 
+        if (_options.MonitorPort > 0)
+        {
+            _monitorServer = new MonitorServer(this, _options, _loggerFactory);
+            await _monitorServer.StartAsync(ct);
+        }
+
         try
         {
             while (!ct.IsCancellationRequested)
@@ -189,6 +197,8 @@ public sealed class NatsServer : IMessageRouter, ISubListAccess, IDisposable
 
     public void Dispose()
     {
+        if (_monitorServer != null)
+            _monitorServer.DisposeAsync().AsTask().GetAwaiter().GetResult();
         _listener?.Dispose();
         foreach (var client in _clients.Values)
             client.Dispose();